Microlithography is used for producing microstructured components such as, for example, integrated circuits or LCDs. The microlithography process is carried out in a so-called projection exposure apparatus including an illumination device and a projection lens. The image of a mask (reticle) illuminated via the illumination device is in this case projected via the projection lens onto a substrate (for example a silicon wafer) coated with a light-sensitive layer (photoresist) and arranged in the image plane of the projection lens, in order to transfer the mask structure to the light-sensitive coating of the substrate.
It is known here to perform in the microlithography process a structure-less illumination (i.e. without use of a structured mask) of the wafer or of the photoresist located thereon in each case after the individual lithography steps for increasing the sensitivity of the photo-resist for the purposes of efficient utilization of the electromagnetic radiation. Only by way of example, it is possible to use UV radiation with a wavelength of 365 nm in the process, wherein the respective illumination of the photoresist which is performed without transferring mask structures is typically effected with an intensity distribution which either is homogeneous or varies over comparatively large spatial wavelengths (e.g. of less than 1 mm) with only small amplitude fluctuations (e.g. less than 10%).
As a result, it is possible due to this additional illumination (which can also be referred to as “post-exposure” of the photoresist) to obtain better utilization of the (e.g. EUV) radiation that is radiated in the actual lithography steps and thus increased throughput of the microlithographic projection exposure apparatus.
Reference is made merely by way of example to S. Tagawa et. al: “Super High Sensitivity Enhancement by Photo-Sensitized Chemically Amplified Resist (PS-CAR) Process”, Journal of Photopolymer Science and Technology, 26, 6, (2013), 825.
In order to be able to perform the above-described additional illumination or “post-exposure” of the photoresist, an additional illumination unit is involved, the configuration of which with respect to the existing desired performance properties in terms of intensity, uniformity and dose stability of the electromagnetic radiation that is coupled into the photoresist during this post-exposure represents an ambitious challenge.